The present technology relates generally to an air fuel mixer for the combustor of a gas turbine engine and, in particular, to an air fuel mixer which uniformly mixes fuel and air so as to reduce NOx formed by the ignition of the fuel-air mixture and minimizes auto-ignition and flashback therein.
Generally, an air-fuel mixer for a gas turbine combustor which provides gaseous and/or liquid fuel to the mixing duct so as to be mixed with air to form a uniform air/fuel mixture. Each of the air-fuel mixers includes a mixing duct, a centerbody fuel injector located within the mixing duct, a set of inner and outer counter-rotating swirlers adjacent to the upstream end of the mixing duct, and a hub separating the inner and outer swirlers to allow independent rotation of the air flow therethrough. However, air flow passing the inner swirler expands and forms a recirculation bubble zone (vortex) around the centerbody. The fuel injected into the recirculation bubble zone tends to have a long residence time allowing liquid fuel to mix with the air flow and causes auto-ignition, thereby damaging components of the air-fuel premixer. Moreover, these dual fuel mixer designs do not include features to adequately extend fuel residence time in the mixing duct for increased fuel-air premixing for low NOx emission without causing auto-ignition or flashback. Thus, while the fuel residence time in the mixing duct must be increased for better fuel-air premixing for low NOx emission, the recirculation bubble zone must be eliminated for preventing auto-ignition and/or flashback from occurring at high power operating conditions.
There is therefore a desire for a system and method premixing fuel and air prior to combustion in a gas turbine engine which better addresses the problems of auto-ignition and flashback while maintaining an emphasis on uniformly mixing liquid and/or gaseous fuel with air so as to reduce NOx formed by the ignition of the air/fuel mixture.